New Physics and Flavour Symmetries

• Antragsteller: Professor Dr. Thorsten Feldmann
• Fachliche Zuordnung: Kern- und Elementarteilchenphysik, Quantenmechanik, Relativitätstheorie, Felder
• Förderung: Förderung von 2012 bis 2019
• Projektkennung: Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 214254430

In the Standard Model (SM) of particle physics different quark and lepton species ("flavours") are only distinguished by their couplings to the Higgs field. Among others this leads to the Cabibbo-Kobayashi- Maskawa (CKM) mechanism which mixes different quark flavours in weak transitions. The successful search for the Higgs particle at the Large Hadron Collider (LHC), and the abundance of experimental data on quark flavour observables from the so-called "'B-factories" conflrm this particular feature of the SM. On the other hand, the observed neutrino oscillations are not explained in the (minimal) SM and already require "new physics" (NP), i.e. particles and interactions beyond the SM framework. In the latter case the energy scale of NP is typically associated with grand unified theories (GUTs) where the tiny values for the neutrino masses are naturally explained through the so-called "see-saw" mechanism. In contrast, the paradigm before the start of the LHC has been that NP at much lower scales is to be expected in order to stabilize the Higgs mass. Ar present, however, no compelling direct evidence for new particles has been observed at the LHC or other collider experiments. In this situation, precision flavour physics provides an alternative strategy to search for indirect effects of physics beyond the SM, and to constrain the masses and couplings of specific NP models. Here, the strong hierarchies observed in the quark masses and mixing play an important role: Namely, if the energy scale for NP is relatively low (i.e. still in the reach of the future LHC searches), the associated flavour structure must be tuned to some degree in order to mimic the CKM mechanism in the SM. In the past, this has been formalized as the principle of minimal flavour violation (MFV). On the other hand, if it turns out that NP effects are generated at sufficiently higher scales, at least some of the MFV assumptions could be relaxed. In this context, flavour symmetries can play an important role. First, they can be used as a guiding principle in the construction of interesting NP benchmark models. Second, they provide a systematic classification scheme of NP flavour scenarios within an effective field-theory approach. The aim of this project is to scrutinize different viable avenues that connect the particular pattern of quark and lepton masses in the SM with the underlying flavour structure of physics beyond the SM. To this end, we are going to systematically analyze the various flavour couplings in the low-energy effective theory. This includes model-independent "benchmark scenarios" characterized by means of flavour-symmetry considerations ("bottom-up" approach), as well as representatives for different types of speciflc NP models ("top-down" approach).

• DFG-Verfahren: Forschungsgruppen
• Teilprojekt zu: FOR 1873: Quark-Flavour-Physik und effektive Feldtheorien